I've seen a lot of people using their PS3 controller to play games on Android like this.

I'm guessing since there is no bluetooth (and I am guessing Wi-Fi direct won't work as well) on the Xbox One controller then wireless play won't be possible, but what about via micro-usb? Would that be possible?

It's something that would be cool, that's all. Not a deal breaker or anything.

That would require someone to develop drivers. We are still waiting for confirmation on whether or not the controllers actually use WiDi for connecting to the console or if the WiDi antenna is for something else like just wireless headsets.

If you read the in-depth look Wired had during the reveal, they confirm the controllers use WiFi direct. That's why they can have true 5.1 audio output through the new headset port since WiFi Direct has a large bandwidth (I believe it's 250 Mbps compared to 3 Mbps for Bluetooth).

But like you said, it all comes down to the drivers. If a device supports WiFi direct, it is theoretically possible for someone to create drivers for it. If not, someone could write a driver to have it work when it's wired (when the micro usb cable is plugged in, it transmits data over the wire).